//
//	The MIT License
//
//	Copyright (c) 2010 James E Beveridge
//
//	Permission is hereby granted, free of charge, to any person obtaining a copy
//	of this software and associated documentation files (the "Software"), to deal
//	in the Software without restriction, including without limitation the rights
//	to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//	copies of the Software, and to permit persons to whom the Software is
//	furnished to do so, subject to the following conditions:
//
//	The above copyright notice and this permission notice shall be included in
//	all copies or substantial portions of the Software.
//
//	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//	IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//	FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//	AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//	LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//	OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//	THE SOFTWARE.


//	This sample code is for my blog entry titled, "Understanding ReadDirectoryChangesW"
//	http://qualapps.blogspot.com/2010/05/understanding-readdirectorychangesw.html
//	See ReadMe.txt for overview information.

#include <list>

template <typename C>
class CThreadSafeQueue : protected std::list<C>
{
public:
    CThreadSafeQueue(int nMaxCount)
    {
        m_bOverflow = false;

        m_hSemaphore = ::CreateSemaphore(
            NULL,		// no security attributes
            0,			// initial count
            nMaxCount,	// max count
            NULL);		// anonymous
    }

    ~CThreadSafeQueue()
    {
        ::CloseHandle(m_hSemaphore);
        m_hSemaphore = NULL;
    }

    void push(C& c)
    {
        CComCritSecLock<CComAutoCriticalSection> lock(m_Crit, true);
        push_back(c);
        lock.Unlock();

        if (!::ReleaseSemaphore(m_hSemaphore, 1, NULL))
        {
            // If the semaphore is full, then take back the entry.
            lock.Lock();
            pop_back();
            if (GetLastError() == ERROR_TOO_MANY_POSTS)
            {
                m_bOverflow = true;
            }
        }
    }

    bool pop(C& c)
    {
        CComCritSecLock<CComAutoCriticalSection> lock(m_Crit, true);

        // If the user calls pop() more than once after the
        // semaphore is signaled, then the semaphore count will
        // get out of sync.  We fix that when the queue empties.
        if (empty())
        {
            while (::WaitForSingleObject(m_hSemaphore, 0) != WAIT_TIMEOUT)
                1;
            return false;
        }

        c = front();
        pop_front();

        return true;
    }

    // If overflow, use this to clear the queue.
    void clear()
    {
        CComCritSecLock<CComAutoCriticalSection> lock(m_Crit, true);

        for (DWORD i = 0; i < size(); i++)
        {
            // semaphore count decrease size, means reset semaphore count
            WaitForSingleObject(m_hSemaphore, 0);
        }

        __super::clear();

        m_bOverflow = false;
    }

    bool overflow()
    {
        return m_bOverflow;
    }

    HANDLE GetWaitHandle() { return m_hSemaphore; }

protected:
    HANDLE m_hSemaphore;

    CComAutoCriticalSection m_Crit;

    bool m_bOverflow;
};
